Soft tissue includes connecting and supporting structures in the body, for example, muscles, connective tissue, adipose tissue and blood vessels. Soft tissue engineering seeks to fabricate replacement parts for soft tissue defects resulting from, e.g., trauma (burns and scars), surgical resection or congenital malformations. In addition, cosmetic use, such as filling of facial wrinkles, is an important application of reconstituted soft tissue.
Alloplastic materials, such as silicon and bovine collagen, have been used in tissue engineering. Such materials may, however, cause severe rejection reactions, as well as allergic reactions. Thus, the use of natural transplant materials is nowadays preferred.
Autologous transplants would be desirable for use in soft tissue engineering. Autologous adipose tissue transplantation is an old therapeutic procedure, where mature adipocytes or adipose tissue itself are transplanted into the site of defect. Adipose tissue is abundant, easy to collect, and readily obtainable for clinical uses. However, the use of autologous adipose tissue transplants may still result in several problems such as resorption, excessive connective tissue (scar) formation, inflammation reactions, as well as hardening and clotting of the transplant. Furthermore, long-term results obtained with adipose tissue transplantation are unpredictable and variable, depending on the method used and the skills of the person executing the method.
Adipose stem cells have been used for soft tissue engineering. Such cells are capable of proliferating and differentiating into mature adipose tissue. However, as the extracellular matrix has an essential role in cell proliferation and differentiation, it is unlikely that repair of large or deep soft tissue defects would be possible with cells alone. In order to be regenerated into functional tissue, transplanted cells need an artificial extracellular matrix, i.e. biomaterial scaffold to aid in cell attachment, proliferation and differentiation.
Formation of new blood vessels, i.e. neovascularization, is crucial for nutrient supply and waste disposal in the regenerating soft tissue. To date, single growth factors (e.g. FGF-2 or VEGF) have been used as bioactive substances for this purpose, but the results have not been satisfactory. It appears that there is a need for a pool of different growth/differentiation factors instead of single factors merely. The right combination of differentiation factors is, however, unknown. Using a pool of bioengineered growth factors in a single implant may result in very high costs.
To date, no adequate approach to the reconstruction of soft tissue defects is available. Thus, there is an acknowledged need in the art to develop implants that induce a rapid volumetric gain to fill defects, maintain the transplanted tissue with no time-dependent volumetric loss, and induce rapid neovascularization.